China DOS Union

The description says it supports large memory and large hard disks, but exactly how large?

Memory is 1MB in real mode, about 3.25GB in protected mode

Maximum hard disk size is 2TB

MSDOS7.1 supports hard disks up to 128G

The maximum hard disk it can support is limited by the BIOS. As for memory, it should be similar.

Originally posted by fujianabc at 2009-1-22 06:18 PM:
Memory is 1MB in real mode, about 3.25GB in protected mode

Maximum hard disk size is 2TB

Exactly.

2TB refers to the partition.
As for the file system = 137G

DOS accesses the hard disk by calling BIOS interrupts, and ordinary BIOSes generally access hard disks using LBA32, so at most it can only support 137G

Originally posted by Sufone at 2009-1-24 01:01 PM:
DOS accesses the hard disk by calling BIOS interrupts, and ordinary BIOSes generally access hard disks using LBA32, so at most it can only support 137G

bios of course supports more than 137GB; generally current bioses can support up to 2TB, otherwise windows wouldn't be able to boot from a hard disk larger than 137GB.

Originally posted by fujianabc at 2009-1-24 20:18:

bios of course supports more than 137GB; generally current bioses can support up to 2TB, otherwise windows wouldn't be able to boot from a hard disk larger than 137GB.

Windows being able to boot from a hard disk larger than 137GB does not necessarily require the BIOS to support hard disks larger than 137G. As long as the starting sector of the partition where your Windows is located is within 137G, and the partition size plus the starting sector does not exceed 137G, Windows can boot normally. After Windows starts, it will drive the hard disk in its own way, and the 137G limit will no longer exist.

Originally posted by Sufone at 2009-1-25 11:33 AM:

Windows being able to boot from a hard disk larger than 137GB does not necessarily require the BIOS to support hard disks larger than 137G. As long as the starting sector of the partition where your Windows is located is within 137G, and the partition size plus the starting sector does not exceed ...

windows needs to get the hard disk size from bios when booting. If bios can't accurately report the hard disk size to windows, windows can't boot normally.

I don't want to argue anymore either; you can try whether DOS can access FAT16/32 partitions beyond 137GB. I've tried it, and there was no problem at all.

Originally posted by Sufone at 2009-1-25 11:33:

Windows being able to boot from a hard disk larger than 137GB does not necessarily require the BIOS to support hard disks larger than 137G. As long as the starting sector of the partition where your Windows is located is within 137G, and the partition size plus the starting sector does not exceed ...

I haven't tried it, but what you're saying is impossible. A lot of people have a single partition on their hard disk, and 500G is 500G. If it couldn't boot, Microsoft wouldn't still be in business...

DOS7.10 really can recognize 3.5G of memory (a little less than Windows, but not by much), which is quite surprising. I suspect DOS is a very low-level operating system, so maybe it has no limit...
As for the hard disk limit, rather than saying it's DOS's, it might be more accurate to say it's FAT32's own...

Originally posted by wl00560 at 2009-1-30 12:49 AM:
DOS7.10 really can recognize 3.5G of memory (a little less than Windows, but not by much), which is quite surprising. I suspect DOS is a very low-level operating system, so maybe it has no limit...
As for the hard disk limit, rather than saying it's DOS's, it might be more accurate to say it's FAT32's own...

The hard disk limit is the BIOS limit. BIOS can only do 32-bit addressing, so the hard disk upper limit is 2^32*512=2^41 bytes, which is 2TB.

Memory is limited by the CPU being 32-bit. DOS is a low-level system; actually, in theory it would also be possible to run x86_64 long mode under DOS, and thus access more than 4GB of memory, but there don't seem to be any DOS programs that need that much memory.